Method of coating aluminum



June 8, 1965 H. w. PEARsALL METHOD OF COATING ALUMINUM Original Filed June 12, 1957 IN VEN TOR Fawazd Z/J IZwasd/ B Y N Y ma RR 3V0 Z OLE am 6 F backing material is relatively costly.

United States Patent Ofiice 3,187,717 METEGD SF CGATENG LUMENUM Howard W. Pearsail, Highiand Paris, Mich, assignor to General Motors (Iorporaticn, Detroit, Mich, a corporation of Delaware Original application lane 12, 1957, Ser. No. 665,282, now Patent No. 3,022,193, dated Feb. 20, 1962. Divide-d and this appiieation dune 27, 1961, Ser. No. 119,899 4 Claims. (Ci. 1118-64) This invention relates to the application of metal coatings to aluminum and aluminum alloy surfaces involving a method which more specifically is particularly suitable for the application of lead base alloys to bearing surfaces of aluminum and aluminum base alloys and an apparatus which can be utilized therewith.

The present patent application is a division of the copending United States application Serial No. 665,282, now United States Patent No. 3,022,193, which was filed on June 12, 1957, and is owned by the assignee of the instant patent application.

Thick layers of babbitt linings on bearings have proved to have comparatively poor resistance to fatigue. However, the fatigue strength of the babbitt lining increases as the thickness of the layer decreases. A babbitt lining of approximately 0.0007 inch has adequate strength for hearing use. Such a thin babbitt layer must be supported by a backing material which is particularly strong and resistant to fatigue and seizure.

Aluminum and aluminum alloys, hereinafter referred to as aluminum, which are in turn supported on a steel backing material, are well suited as backing materials for babbitt linings. Backing members formed of such metals are light in weight, yet have adequate strength and sufficient resistance to fatigue and seizure. The use of aluminum base backing materials is particularly advantageous due to the good bearing properties of aluminum itself. Thin linings of the babbitt metal alloy with the aluminum surface to provide a bearing of superior quality. Aluminum base alloys which possess particularly good bearing qualities include an alloy consisting essentially of 0.3% to 11.0% silicon, 0.05% to 5% cadmium and the balance aluminum, and an alloy consisting essentially of 0.05% to 3% magnesium, 0.3% to 11% silicon, 0.05% to 5.0% cadmium, 0.1% to 2.25% chromium and the balance aluminum.

In the past smooth, adherent coatings of babbitt metal on steel backing members have been obtained by electrodepositing babbitt metal directly onto the steel backing. Electrodeposition has heretofore been the most satisfactory commercial method of applying babbitt to an aluminum backing material. Unfortunately, due to the rapid formation of an oxide coating on aluminum surfaces, it is exceedingly difiicult to obtain electrodeposition of babbitt metal directly onto aluminum. Therefore, the aluminum surface requires extensive pretreatment before receiving the babbitt. The backing member normally is first immersion-coated with zinc, and then given a flash coating of copper, the babbitt metal being electrodeposited onto the fiash copper layer. A thin layer of tin is then usually electrodepositecl onto all the surfaces of the bearings. This method ofapplying babbitt to an aluminum In addition, the presence of zinc and copper in the overlay of' the aluminum surface, although necessary for adherence of the electroplated babbitt, has proved in some instances to be detrimental to bearing performance.

It is, therefore, a principal object of this invention to provide a method for directly coating aluminum by means of a fused chloride or bromide of a metal below aluminum in the electromotive series. Another object of this invention is to provide a method of joining aluminum parts using such a coating. More specifically, another object comprehened by this invention is to provide an apparatus and process whereby aluminum bearing backing members may be directly coated with a thin layer of babbitt metal.

Other objects,'advantages and features of the present invention will appear more clearly from the following description of preferred embodiments thereof and from the drawing which shows a schematic vertical view in partial section of an apparatus which can be used to practice the process described herein.

In accordance with the invention, the aluminum surface is covered with a layer of a powdered chloride or bromide of a metal below aluminum in the electromotive series, and the composite article is thereafter heated to the fusion temperature of the salt. More particularly, I have employed chlorides and bromides of lead and tin to provide satisfactory results in an expeditious manner. At

the temperature required to fuse the salt, a displacement reaction occurs wherein the metal of the salt is reduced to the pure metal and deposited on the aluminum surface. The chlorine or bromine of the salt combines with the aluminum to form a volatile aluminum halide which escapes by vaporization. The fusion temperature of some otherwise satisfactory salts is often undesirably high, such as that of lead chloride which is about 934 F. However, the temperature required to fuse this salt may be reduced to about 750 F. by employing an approximately eutectic mixture of the desired metal salt and other suitable salts, such as potassium chloride and sodium chloride. An example of such a mixture is one consisting of about 68% plumbous chloride, 18% potassium chloride and 14% sodium chloride.

It has been found that the addition of the potassium chloride and sodium chloride not only reduces the temperature required to melt the desired salt but also promotes wetting of the aluminum surface, thereby assisting in the. 7 formation of a more adherent coating of the desired metal. In connection with this latter function, it is often desirable to add a small amount of these salts in excess of that required to form a eutectic mixture. For example, in coating aluminum with a mixture of metals, as noted hereinafter, small excess amounts of sodium and potassium chlorides do not significantly increase the fusion temperature yet provide desirable additional wetting action. The potassium and sodium chlorides, which do not form part of the coating, rise to the surface of the coating during fusion, and subsequently can be washed therefrom with water after cooling ,of the coated article.

if it is desired to coat an aluminum'surface with a combination of metals, this end may be accomplished by employing amixture of the appropriate metal chlorides or bromides, e.g., PbCl and SnCl Coatings composed of two or more metals also can be applied by employing a mixture of a powdered pure metal and a metal chloride or bromide. The mixtures tin powder and PbCl as well as lead powder and SnCl have efficaciously been emr ployed to practice this modification of the invention. The

hereinbeforementioned eutectic forming salts can also be employed in the mixture to apply' these coatings when it is desirable to utilize'the lower melting point and the wetting effect produced by the potassium and sodium chlorides.

It has been found that such a powdered mixture as described above cannot be conveniently applied to an inclined surface. 7 However, if a small amount of an organic polymer with adhesive properties, such as nitrocellulose or acrylic resin, is incorporated in the powdered mixture, the resulting mixture will adhere to an inclined surface as firmly as to a horizontal surface.

Patented June 8, 1965 The present invention also comprehends coating aluminum by immersing it into a bath of the molten metal on which the molten chloride or bromide salt of that metal is floating '(e.g., lead and PbClz). The aluminum is pref erably preheated and dipped into this bath, whereupon the metal (e.g., lead) deposits onto the aluminum. The melting point of the halide salt can be suitably lowered, as previously indicated, by employing a eutectic mixture of potassium and sodium chlorides. The coating of aluminum with an alloy can be accomplished employing a bath of this type simply by incorporating in'the bath the appropriate metals with their corresponding chloride or bromide salts in the supernatant molten salt layer.

A further modification of the present invention is the coating of babbitt metal directly onto aluminum bearings. A powdered mixture such as hereinbefore described is suspended in a highly volatile liquid, forming a slurry, and sprayed onto a heated aluminum surface. The

Percent Lead chloride 56.5

Sodium chloride 11.8 Potassium chloride 15.0 Cuprous chloride 12.5 Tin powder 4.5

The above dry ingredients are passed preferably through a 200 mesh screen, mixed together'in a ball mill with a suitable volatile liquid, such as lacquer thinner, in a pro portion of one part by weight of dry solids to one and one-half parts of lacquer. thinner. The slurry formed thereby is sprayed onto the surface of the bearings and, as the volatile liquid evaporates, the solids of the slurry are deposited on the bearing surface. This layer of solids can be built up to a substantial thickness through successive sprayings of slurry on warm bearings, each layer being permitted to dry before the succeeding layer isapplied. Thus, it is possible to obtain correspondingly thickermetallic coatings after fusion of the mixture.

Occasionally, a particular coating mixture does not produce a satisfactory metal deposit when the coating mixture has been built up to a substantial thickness. It

was found that incorporation of an organic adhesive, for 7 example nitrocellulose lacquer, in such coating mixtures permitted thickerdeposits of the metallic coating to be prepared which were suitable for bearing use, When an adhesive was included in the following composition, it permitted a substantial increase in the thickness of the coating mixture which c'ould be applied to produce a satisfactory thicker metallic coating:

This mixture is passed preferably through a 200 mesh screen and combined with approximately 12 parts adhesive to 100 parts of the above mixture by weight. Sufiioient lacquer thinner is then added to comprise a final slurry of about to lacquer thinner;

Referring more particularly to the drawing, the apparatus. shown can be used to coat bearings in accordance withjthe invention. The apparatus. comprises a cylindrical'vertical column 10 ofv any suitable refractory material. This column includes a bearing spray section 12,

tubular members.

bearing firing section 14, and a bearing cooling section 16. Semi-cylindrical bearing sleeves 18 are introduced in pairs into the column through the upper opening 19.

Two conveyers 2t) and 22, arranged generally opposite one another at the upper opening 19 of the. column 10, carry the bearing sleeves to the top of the column. The sem'i cylindrical bearing sleeves are placed in the top of the column with their inner cylindrical surfaces facing one another, their ends being in general abutment,

thereby forming a generally cylindrical inner bearing surface. The positioning of thebearing sleeves at the top of the column is aided by a frusto-conical skirt 24 projecting upwardly from the opening 19 of the column 10.v The alignment and positioning of the bearing sleeves within the column may be assisted, by indentations 21 on the inner surface of the column and suitably positioned tangs 23 as shown in FIGURE Z on the outer surface of the sleeves which engage the indentations 21 of the column.

' The bearings progress downwardly through the column under force'of gravity, the rate of such progression being determined by the speed of an automatic bearing support and take-off or removal device 25 located at the bottom of the column. A downwardly depending second frusto-conical skirt 26 also can be. employed at the bottom of the column to assist in the proper positioning of the bearing as it emerges from the loweropening 27. The bearings can be supported at the lower end of the vertical column by any suitable device which will also permit the lowering of the bearings in the column and a removal therefrom. A preferred form for such a device is the toothed wheels 28 and 30 located at the lower end of the vertical column as shown. The semi-cylindrical bearing sleeves are supported by teeth 31 on the outer periphery of, the wheels and automatically lowered as the wheels revolve. An adjacent tooth 33 on the wheel then engages the next bearing sleeve to separate it from the one above it and in doing so projects under the lower edge of the bearing thereby supporting it.

A rotatably mounted air tube 32 for introducing dry air into the interior of the column is positioned within the upper part of the column coincidentally with'the axis of thereby permitting free passage of the bearings down the column. The interior of the hollow metal disk communlcates with the interior of the tube 32. The upper and lower walls of the disk 34 are provided with apertures 36,. forming inlet openings, through which dry air, introduced into the tube 32 at its upper extremity 38,'passes and enters the interior of the column.

' Surrounding an upper portion of the air tube is a second tube 40 of larger diameter rotatably mounted at its upper end and having its'side wall 42 spaced fromthe wall 44 of the air tube 32, thereby forming an annular space 46 therebetween. A non-rotatable cover 48 is positioned over the upper open end of the outer tube 40 surrounding the inner tube 32 and is suitably sealed, forming an upper wall for the annular space 46 defined by the A lower wall for the annular space 46 is formed by sealing the lower end 50 of the outer tube to the wall 44; of the air tube 32.. The lower end of the outer tube 40 can be sealed in any suitable manner capable of withstanding the heat of the column and the detrimental effect of vapors present in the column, a preferred seal being obtained by welding. Its ends, being thus sealed, the annular space 46 defined by the tubular mem bers forms anannular chamber.

The coating slurry, a suspension of metal chlorides or bromides and a powdered metal in a highly volatile liquid, is introduced under pressure by a suitable pump 52 intothe annular chamber 46 through the cover 48. Several small vertically aligned orifices 54 in the outer tubes are located adjacent its lower end 50. The slurry of the coating mixture is sprayed under pressure through these orifices onto the inner vertical surfaces of the bearings.

The outer tube 40 and the air tube 32 are rotated by means of a motor 56 communicating with a spur gear 58 secured to the outer periphery of an'upper part of the outer tube. As the slurry mixture is pumped into the slurry chamber, the tubes are rotated and the slurry is spayed under pressure from the orifices 54 while the tubes are rotating. The bearing sleeves 18 progressing down the tube are the therefore coated with the slurry by means of the rotating spray.

Surrounding the bearing spray section 12 of the column is a suitable heating device, preferably a spiral electric resistance heater 60. The resistance heater 60 is connected to an appropriate source of electrical current (not shown) so that the upper portion 12 of the chamber may be warmed to approximately 300 to 400 F Around the bearing firing section 14 of the column 10 beneath the upper Warming heater as is another heater, preferably spiral electric resistance heater 62 which when connected to a suitable source of electrical current (not shown) is capable of raising the interior temperature of the encircled portion 14 of the column to approximately 725 to 825 F. Immediately below the bearing firing section is the bearing cooling section 16 of the column. Surrounding this portion of the column is a cooling coil 64 which is connected to a source of coolant (not shown), preferably water. It is desirable that the cooling section of the column reduce the temperature of the bearing to approximately 400 F. or less before it emerges from the column.

The bearing sleeves 13, prior to coating with the babbitt metal, are degreased and cleaned in a conventional manner and thereafter dried. The bearings are then placed on the conveyers 20 and 22 which introduce the semicylindrical bearing sleeve halves 18 into the top of the column where they are warmed to about 350 F., preferably in the presence of dry air, although either nitrogen or incompletely dried air is also fairly suitable.

The inlets 36 for admission of the dry air into the chamber are located between the spray section 12 and the firing section 14 so that the combustible volatile liquid vapors are blown upwardly out of the column and the corrosive aluminum chloride vapors formed in the firing section are carried out the lower openingZ'i.

As the bearings progress down the column, they are warmed by the heating coil 60 around the outside of the column. The warmed bearings are then coated with a suitable slurry mixture by means of the rotating spray. During the progression down the column, the caking and building up of the coating mixture correspondingly progresses due to the action of the rotating spray.

The bearings are then subjected to the heat of the firing section 14 wherein the temperature is raised to approximately 800 F. The exact temperature preferred for the firing section will depend upon the melting point of the coating mixture employed. It is advantageous to have the temperature slightly above the melting point of the salt mixture but not high enough to cause any damage to the aluminum. Generally, the mixtures employed for coating lead base alloys will have a melting point between approximately 725 and 825 F. After the hearing has been fired for a sufiicient length of time to complete reduction of the babbitt metal, the bearing progresses to the cooling section 16 of the column which reduces the temperature of the bearing to generally 400 F. or less. Cooling of the bearing in dry air prevents corrosion, which would occur if the hot bearings were introduced into moist air. The cooled bearing is removed from the column and preferably washed in a suitable soap solution. Simultaneous scrubbing with a fiber brush also aids in removing any excess metal salts still remaining in the babbitt coating.

The present method of bonding a metal to an aluminum surface may also be employed as a means to join aluminum surfaces to each other. Coating mixtures, such as material having generally equal parts by weight of lead and zinc.

As hereinbefore indicated, it is not always convenient to employ a dry powdered mixture for the bonding, for example, when coating an inclined aluminum surface. In such instances, it is advantageous to apply the coating mixture as a paste or slurry which is formed by adding to the powdered mixture a suitable amount of a volatile liquid such as water, alcohol, lacquer thinner, etc. Suitable salts of other metals below aluminum in the electromotive series can also be included in the mixture if it is desirable to employ a solder of a different composition than specified above. It is understood that eutectic mixtures, such as hereinbefore described, can also effectively be employed in joining aluminum parts by this method.

Although the present invention has been described in conjunction with preferred embodiments thereof, it is understood that variations and modifications may be found which are obvious to those skilled in the art. It is not intended that these preferred embodiments be a limitation of the scope of the invention except as limited by the appended claims.

I claim: I

1. An apparatus for providing a thin coating of a bearing metal on interior bearing surfaces'of aluminum bearing members, said apparatus comprising a chamber having inlet and outlet openings, means associated with said chamber for conveying aluminum bearing members into said inlet of said chamber, means supporting and regulating continuous movement of the bearings through said chamber, a first heating means for warming said bearing members to approximately 300 F.400 F. in said chamber adjacent said inlet opening to said chamber, means for spraying a coating mixture solely onto said interior bearing surface of said warmed bearings as said bearings are moved continuously through said chamber, a second heating means adjacent said first heating means for heat- 0 ing said coating mixture and fusing the same on said bearing members, and cooling means adjacent said second heating means to effect cooling and solidification of the coating mixture after fusion.

2. An apparatus for providing a thin coating of a bearing metal on interior bearing surfaces of aluminum bearing members, said apparatus comprising a chamber having entrance and exit openings therein, means associated with said chamber for conveying aluminum bearing members into said entrance of said chamber, means for supporting and regulating continuous movement of said bearing members through said chamber, means to introduce a gas into the interior of said chamber, means for spraying a coating mixture solely onto said interior bearing 3. An apparatus for providing a thin coating of a bearing metal on interior surfaces of aluminum bearing members, said apparatus comprising a tubular vertical column having its upper and lower ends open, two diametrically opposed conveyors for simultaneously introducing semicylindrical aluminum bearing sleeves into the upper opening of said column, a bearing sleeve support and movement regulatory device located at the lower end of said column to regulate the progression of said bearing sleeves down said column, a first heating means positioned around an upper. portion of said column to form a warming section in said column for said bearing members as they are introduced into said column, a rotatably mounted spray means in said warming section ofsaid column to, spray a coating mixture onto said bearing members, a second heating means around said column located below said first heating means for heating a portion of said column immediately below said warming section to a temperature sufficient to fuse said coating mixture, means tointroduce dry air into said column between said heating means, and cooling means around said column adjacent and below said second heating means to cool and solidify the fused coating mixture.

4. An apparatus for providing a thin coating of a hearing metal on interior, surfaces of aluminum bearing members, said apparatus comprising a tubular vertical column having its upper and lower ends open, two diametrically opposed conveyors for simultaneously introducing semieylindrical bearing sleeves into the top of said column, an upwardly projecting conical skirt disposed in theupper opening of said column, said sldrt being spaced from and coaxial with the Walls of said vertical column, a bearing sleeve and take-off device. located at the lower opening of said column to support and regulate the progression of the bearing sleeves down said column, a spiral electric resistance heater located around the upper portion of said column to form a warming section in said column, a first rotatably mounted tubular conduit for conveying dry air into said column positioned coaxially within said column and extending downwardly from the upper opening of said column, said conduit communicating at its lower extremity with a hollow apertured disk-like member disposed immediately below said Warming section, a second rotatably mounted tubular conduit disposed around and spaced from the upper part of said first conduit forming an annular space therebetween, the ends of said second tubular conduit suitably sealed forming upper and lower walls to the annular chamber defined by said conduits, saidsecond tubular conduit having a plurality of vertically aligned apertures therein near its lower end from which a coating mixture is sprayed, a second spiral electric resistance heater around said column adjacent and immediately below the first, heating the encircled portion of said column generally to the fusion temperature of the coating material applied to said bearing sleeves.

References Cited by the Examiner UNITED STATES PATENTS 2,241,789 5/41 Queneau et al 117-105 2,676,895 4/54 Russell 11864 X 2,700,624 1/55 Wagner et al 11858 2,761,793 9/56 Brennan 11869 2,833,667 5/58 Dalton 117105 RICHARD D. NEVIUS, Primary Examiner. 

1. AN APPARATUS FOR PROVIDING A THIN COATING OF A BEARING METAL ON INTERIOR BEARING SURFACES OF ALUMINUM BEARING MEMBERS, SAID APPARATUS COMPRISING A CHAMBER HAVING INLET AND OUTLET OPENINGS, MEANS ASSOCIATED WITH SAID CHAMBER FOR CONVEYING ALUMINUM BEARING MEMBERS INTO SAID INLET OF SAID CHAMBER, MEANS SUPPORTING AND REGULATING CONTINUOUS MOVEMENT OF THE BEARINGS THROUGH SAID CHAMBER, A FIRST HEATING MEANS FOR WARMING SAID BEARING MEMBERS TO APPROXIMATELY 300*F.-400*F. IN SAID CHAMBER ADJACENT SAID INLET OPENING TO SAID CHAMBER, MEANS 